An attempt is made to identify the precise origin of the effect of alloying additions on the discontinuous precipitation kinetics with trace additions of Sb (0.26 at%) and Cd (0.16 at%) to a Pb—9.87 at% Sn alloy. Extensive resistometric measurement of the precipitation kinetics, duly substantiated by microstructural observations at appropriate stages, evidences that the drastic reduction (>50%) in the reaction rate can be attributed neither to the atomic size nor the valence electron difference caused by the Sb or Cd addition. Segregation of the ternary elements at the sweeping reaction fronts appears to retard and ultimately terminate the discontinuous precipitation process at a premature stage.